The present invention relates to the field of machine-building and, in particular, to a continuously variable transmission and may be used in various fields of technology in cases where it is necessary to ensure continuously variable torque transmission while adjusting the transmission ratio depending on a load at the transmission output. It may be used, in particular, for means of transportation and variable-speed drive units.
At present, continuously variable transmissions made on the basis of a friction variable-speed drive are of wide use.
Known in the art is a planetary friction variable-speed drive comprising the outer central friction discs and the intermediate conical friction discs as well as the pressure members that apply an axial action to the central friction discs and the intermediate conical discs arranged therebetween, a radial movement of the intermediate discs and associated change in the transmission ratio of the variable-speed drive taking place due to applying an axial action to the said discs. Thus, the pressure members are at the same time mechanisms changing the transmission ratio. GB Patent 1384679, IPC6 F16H 15/50, 1975.
The closest to the claimed solution under the first variant as to the technical substance and achieved result is a continuously variable transmission comprising a planetary friction variable-speed drive consisting of the inner and outer central friction discs laterally embracing the intermediate friction discs, a mechanism for combined modification of the transmission ratio and of the pressure made in the form of rotating levers carrying the intermediate friction discs and arranged on the planetary variable-speed drive carrier with the possibility of changing the position of the rotating levers. Patent RF 2091638 IPC6 F16H 15/52, 1997 (the prototype). In the known solution the mechanisms for combined modification of the transmission ratio and of the pressure press the central friction discs to the intermediate discs with forces proportional to transmitted torques, subject to pre-pressing by springs.
The prototype transmission has several inherent deficiencies, namely:
the pressure members of the mechanism for combined modification of the transmission ratio and pressure are complex, and, what is most important, they do not solve the task of optimal pressing the discs to each other due to the fact that the friction coefficient at the points of the friction oil contact is varied greatly; according to the results of the study performed by the author the value of this coefficient for the central inner friction discs is varied in the range from 0.015 to 0.03 and for outer ones
from 0.02 to 0.08; therefore the pressure, which is proportional to the torque only, does not achieve the required result in the planetary systems;
the systems of pressure members of the said mechanisms, including automatic adjustment with pre-pressing by a spring with a force that is usually corresponds to 25-35% of the maximum force, also do not achieve the required result; there the initial working adjustment for an outer central friction disc should be app. 5-7% of the maximum force, and even that, the most complex, combined system creates the pressure 5 times greater than the necessary one and leads to a sharp reduction in the efficiency, but for a car transmission this working mode is most widely used, especially when moving along a road (at the highest transmission);
the friction coefficient depends heavily on the rotation speed of the variable-speed drive shafts, and the above pressure members system do not enable to correct it.
The closest to the claimed solution under the second variant as to the technical substance and achieved result is a continuously variable transmission comprising a planetary friction variable-speed drive consisting of the inner and outer central friction discs laterally embracing the intermediate friction discs, a mechanism for combined modification of the transmission ratio and of the pressure made in the form of rotating levers carrying the intermediate friction discs and arranged on the planetary variable-speed drive carrier with the possibility of changing the position of the rotating levers by pushers moved along guides. Patent RF 2091637 IPC6 F16H 15/52, 1997 (the prototype).
A specific feature of the invention according to the prototype is that the pushers are spring-loaded to the guides by centrifugal forces created due to the unbalanced state of the rotating levers relative to their rotation. Such implementation creates very inconvenient conditions of loading the pushers, resulting in inaccuracy and low reliability of regulation. For example, given the rotation speed of a low-speed shaft is changed tenfold (this is the real range of a variable-speed drive transmission-ratio variation), the centrifugal force varies hundredfold, the torque xe2x80x9cexerting a counter-actionxe2x80x9d to that force in the regulation system varies approximately tenfold, and the maximum torque, which on a low-speed shaft corresponds to the minimum rotation speed, will just correspond to the minimum centrifugal force. Practical studies have showed that such a system does not ensure the necessary accuracy of the transmission-ratio regulation.
The objective of this invention is to create a continuously variable transmission on the basis of a variable-speed friction disc drive having a higher efficiency, durability, reliability and convenient in operation due to simplifying the design of the mechanism for combined modification of the transmission ratio and pressure, ensuring compliance of the friction discs pressure force in different operation modes with the transmission ratio value as well as due to dependence of the variable-speed drive transmission ratio on the output shaft load.
According to the first variant, in order to achieve the said technical result in a known continuously variable transmission comprising a planetary friction variable-speed drive consisting of the inner and outer central friction discs laterally embracing the intermediate friction discs, a mechanism for combined modification of the transmission ratio and of the pressure made in the form of rotating levers carrying the intermediate friction discs and arranged on the planetary variable-speed drive carrier with the possibility of changing their position, the mechanism for combined modification of the transmission ratio and of the pressure is provided with power members applying an axial action, which are arranged on the end sides of the inner and outer central friction discs so as to ensure their contact in the annular areas opposite to the annular areas of contact between the inner and outer central friction discs and the intermediate friction discs, an average axial rigidity of the power members applying an axial action, which are brought into contact with the outer central friction discs, is made so as to be higher, in terms of absolute value, than an average axial rigidity of the power members applying an axial action, which are brought into contact with the inner central friction discs.
Some other embodiments of the first variant of this invention are possible, according to which it is advisable that:
a mechanism for combined modification of the transmission ratio and the pressure would be provided with support members arranged on the central shaft and on the epicycle on the rear side of the power members applying an axial action and made with the stops contacting the power members applying an axial action with the possibility of varying their axial rigidity both in magnitude and in negative/positive value;
each power member applying an axial action, as included in the mechanism for combined modification of the transmission ratio and the pressure, would be made in the form of a chamber communicating with the pressurized working medium and arranged on an epicycle with the possibility of pressing of, at least, one outer central friction disc to the respective intermediate friction discs depending on the working medium pressure in the said chamber;
each power member applying an axial action would be made in the form of an annular conical surface made on a power member arranged on the central shaft and on an annular conical surface facing it and made on an inner central friction disc, between the said annular conical surfaces weights being arranged with the possibility of their radial movement along a conical gap formed by the said annular conical surfaces and with the possibility of varying the value of pressing the inner central friction discs to the intermediate friction discs;
the said weights would be made in the form of shaped spring rings with alternating radial slots.
The said features are essential and interrelated therebetween by cause-effect relation with the formation of a totality of essential features sufficient for achieving the technical result.
This is ensured by the fact that the central friction discs, both the inner and the outer ones, are pressed to the intermediate friction discs by the power members applying an axial action, in particular by springs made in the form of well-known plate or cantilever beam discs arranged on either side of the intermediate friction discs both on the outer and the inner central friction discs. The said springs interact with the said discs on the back surfaces at the radii that are closer to the races than to the disc bases.
The inner and outer central friction discs themselves may serve as such springs, in such a case the average, over the total travel, rigidity value of the springs of the outer central friction discs in terms of absolute value (since such value may be varied from positive values to zero and further to negative values) is higher than the similar parameter of the springs of the inner central friction discs. The rigidity of the springs of the outer or inner central friction discs may be varied in their travel smoothly or discretely, and the said springs may contact by their face or back surfaces with the stops or other springs with the possibility of varying the rigidity of the first springs of the inner and outer central friction discs. In order to correct the force of pressing the inner and outer central friction discs to the intermediate friction discs, the continuously variable transmission is provided with pressure adjusters acting according to the rotation speed and made in one variant of this invention in the form of weights arranged between the annular conical surfaces made on the support members and on the inner central friction discs and installed with the possibility of increasing the pressure force while the rotation speed is increased, as well as in the form of chambers for supplying the pressurized working medium (e.g., gas or liquid), which also increases the pressure force, maintaining it at a required level.
Thus, the optimal, as to the efficiency, pressing the outer and inner central friction discs to the intermediate friction discs is ensured, which is conditioned, e.g., by the fact that the torque, in particular that developed by car engines in the full fueling mode without enrichment (the most economical mode in which a continuously variable transmission should work), is close to a constant value, and the torque on the carrier of a variable-speed drive (output torque) depends on the variable-speed drive transmission ratio that is rather accurately related to the radial movement of the axle of the intermediate friction discs, and, therefore, to the axial travel of the spring. Thus, each movement of the intermediate friction discs corresponds, due to a certain change in the spring position, a well-defined optimal pressure force slightly distorted by a change in the rotation speed. Such a change, which results in some insignificant change of the friction coefficient, may be corrected with the adjusters introduced into the continuously variable transmission, such adjusters having centrifugal weights or pressure chambers creating an additional pressure force.
The engine of a transportation vehicle works under low fueling, according to modern methods of automatic control of the car power unit with the known continuously variable transmission, only at the start and at low movement speeds. In those modes the variable-speed drive efficiency, according to calculations and experiments, is reduced not more than by 1-3% due to a non-optimal pressure force (overpressure), which is not likely to be noticed compared to a far more noticeable reduction in the engine efficiency under low fueling. The efficiency of the claimed continuously variable transmission with the proposed system of exerting elastic pressure on the friction discs is most applicable for variable-speed drives according to the given system and reaches 0.96-0.97 at the highest transmission ratios of 1.2-1.3.
According to the second variant, in order to achieve the said technical result in the known continuously variable transmission comprising a planetary friction variable-speed drive consisting of the inner and outer central friction discs laterally embracing the intermediate friction discs, a mechanism for combined modification of the transmission ratio and of the pressure made in the form of rotating levers carrying the intermediate friction discs and arranged on the planetary variable-speed drive carrier with the possibility of changing their position, a mechanism for combined modification of the transmission ratio and of the pressure is provided with pushers arranged with the possibility of moving along the guides, members applying pressure to the rotating levers and power members applying an axial action arranged on the face sides of the inner and outer central friction discs so as to ensure their contact in the annular areas opposite to the annular areas of contact between the inner and outer central friction discs and the intermediate friction discs, an average axial rigidity of the power members applying an axial action, which are brought into contact with the outer central friction discs, is made so as to be higher, in terms of absolute value, than an average axial rigidity of the power members applying an axial action, which are brought into contact with the inner central friction discs, and the said pressure members being connected to the rotating levers with the possibility of ensuring the rotation of the said levers to the side corresponding to the reduction in the transmission ratio from the central shaft to the low-speed shaft.
Some other embodiments of the second variant of this invention are possible, according to which it is advisable that:
the transmission would be provided with a driven mechanism connecting the carrier with the low-speed shaft and made, in particular, as a driven jaw clutch;
the guides would be made as helical profiled surfaces, which direction would ensure, if the carrier advances the low-speed shaft in case of making the central shaft the driving one and making the low-speed shaft the driven one, an angular movement of the rotating levers to the side corresponding to an increase of the transmission ratio;
the pressure members of the rotating levers would be made as, at least, one spring connected on one its end to the carrier and on the other end to the low-speed shaft;
the pressure members of the rotating levers would be made as, at least, one spring connected on one its end to the low-speed shaft and on the other end to the rotating levers having the capacity of moving angularly with respect to the carrier;
the pressure members of the rotating levers would be made as, at least, one spring connected on one its end to the carrier and on the other end to the rotating levers having the capacity of moving angularly with respect to the carrier;
the rotating levers would be made imbalanced, their center of gravity would be displaced from their axles of rotation to a side according to which its movement from the center to the periphery results in a reduction in the variable-speed drive transmission ratio;
the pressure member would be made with the possibility of regulating the dependence of the force magnitude on movement, e.g., as power hydraulic or pneumatic cylinders;
the profiled surfaces would be made with the profile varying in the axial direction and would be arranged with the possibility of their axial movement with respect to the pushers;
the profiled surfaces and the pushers may be arranged both at the rotating levers and at certain parts of the mechanism for modification of the transmission ratio and the pressure, which are connected to the low-speed shaft.
The said features are essential and interrelated therebetween by cause-effect relation with the formation of a totality of essential features sufficient for achieving the technical result.
Namely, in a case the mechanism for modification of the transmission ratio and the pressure comprises the pressure members of the rotating levers (e.g., springs, hydraulic cylinders or pneumatic cylinders, etc.), it ensures their pressing to the direction of turning that corresponds to a decrease in the transmission ratio from the central shaft to the low-speed shaft, the pushers and the guides profiled surfaces may be arranged both at the rotating levers and at the member connected to the low-speed shaft; the said profiled surfaces are made helical in the direction that ensures, if the carrier advances the low-speed shaft in case of making the central shaft the driving one and making the low-speed shaft the driven one, an angular movement of the rotating levers to the side corresponding to an increase of the variable-speed drive transmission ratio; the profiled surfaces may be made varying (non-flat) in the axial direction with the possibility of their angular movement with respect to the pushers; the center of gravity of the rotating levers either may be at the axle of their rotation (the levers are balanced) or may be displaced to the side according to that its movement from the center to the periphery results in a decrease in the variable-speed drive transmission ratio; if necessary the mechanism for modification of the transmission ratio and the pressure may be fixed while the variable-speed drive transmission ratio is maintained constant. In such a case both the said central shaft and the low-speed shaft may be either driving or driven, respectively.